Lateral insulated gate controlled transistors have been proposed in which a gate is used to control the conductance of an inherent bipolar transistor. An example of one such device is shown in FIG. 1 of this application and an equivalent circuit derived from the device is shown in FIG. 2. FIG. 1 is based on U.S. patent application Ser. No. 803,049 for "A Lateral insulated Gate Transistor With Improved Latch Up Immunity" assigned to the assignee of the present invention. In these structures, the MOS channel controls the base current to the vertical and lateral bipolar transistor elements. The base current promotes carrier injection from the common anode to both the lateral and vertical transistors and the long drift region, required to support voltage during the off-state of the device, gets conductively modulated. The degree of conductivity modulation depends upon the base drive. This insulated gate channel resistance reduces the amount of base drive that can be supplied to the base of the inherent bipolar transistor and consequently impairs the degree to which the inherent bipolar transistor can be turned on. In the insulated gate structures heretofore known, while the inherent transistor has been activated, the inherent transistor has not been fully turned on under conventional operation conditions due to a lack of sufficient base drive. More particularly, in typical lateral insulated gate transistors, the inherent bipolar transistor is believed to operate at between 40% and 50% of its capacity.
Thus an unfulfilled need exists to provide a lateral insulated gate semiconductor device which fully utilizes an inherent bipolar transistor structure under normal operating conditions.